Method for checking the operativeness of a tank-ventilation valve of a tank-ventilation system

ABSTRACT

A method for checking the operativeness of a tank-ventilation valve of a tank-ventilation system of a motor vehicle is characterized by the following steps: the tank-ventilation valve is triggered in a stepped manner in a preselectable working point; the intake-manifold pressure (p intake manifold ) is measured and modeled in the process; the measured intake-manifold pressure (p intake manifold ) is compared to the modeled intake-manifold pressure and an operative tank-ventilation valve assumed if a correlation within preselected limits is given; otherwise, a defective tank-ventilation valve is assumed.

FIELD OF THE INVENTION

The present invention relates to a method for checking the operativenessof a tank-ventilation valve of a tank-ventilation system of a motorvehicle.

BACKGROUND INFORMATION

The tank-ventilation valve of a tank-ventilation system of a motorvehicle, constituting a component that influences the exhaust gas, mustbe checked for its operativeness within the framework of the on-boarddiagnosis (OBD). From the German Published Patent Application No. 41 22975 a method for ascertaining the operativeness of a tank-ventilationsystem can be gathered in which the signals for the volume flow of thetank-ventilation valve and the signals for the pressure differentialbetween the tank interior and the ambient pressure are subjected to across-covariance analysis. The mentioned signals are formed by a highpass prior to the generation of the cross-covariance function, and themaximum or the averaged value of the cross-covariance function withrespect to the product of the two input variables is calculated. Avariance measure is generated for the signal of the volume flow throughthe tank-ventilation valve and a transmission coefficient calculatedfrom the variance measure and the averaged value or maximum. If thetransmission range is within a predefined range, the tank-ventilationsystem is considered operative. One advantage of this method is itsindependence from tank-pressure variations that are not due to changesin the volume flow through the tank-ventilation valve. Specifically,these are changes that are attributable to sudden gas formation in thetank, such as may be caused by sloshing fuel.

It is also known to implement the check of the tank-ventilation valve bycontrolling the tank-ventilation valve in idling in a sufficientlystable working point. Simultaneously, the change in the mixturecomposition and the change in the energy flow via the throttle valve,which represents the product of the air-mass flow via the throttle valveand the ignition-angle efficiency factor, are observed. Conclusionsconcerning an operative tank-ventilation valve are drawn as a functionof this observation. It is problematic here that the check may beregistered as a distraction by the driver of the vehicle, for examplewhen a change in the rotational speed occurs.

SUMMARY OF THE INVENTION

It is an object of the present invention to further develop a method forchecking the operativeness of a tank-ventilation valve of the typementioned in the introduction, in such a way that the check procedure isnot noticed by the driver of a motor vehicle and, in particular, thatthe check may also be implemented outside of idling.

To solve this objective, the method of the present invention forchecking the operativeness of a tank-ventilation system of a motorvehicle is characterized by the following steps:

-   the tank-ventilation valve is triggered in a pulsed manner in a    preselectable working point;-   the intake-manifold pressure is measured and modeled in the process;-   the measured intake-manifold pressure is compared to the modeled    intake-manifold pressure and an operative tank-ventilation valve    assumed if a correlation within predefined limits is given;    otherwise, a defective tank-ventilation valve is assumed.

Due to the pulsed triggering of the tank-ventilation valve, there isvery low interference potential, which is virtually undetectable by thedriver. Moreover, in contrast to other known methods for checking theoperativeness of the tank-ventilation valve, a check of thetank-ventilation valve is also possible outside of idling.

A frequency analysis of the measured and modeled intake-manifoldpressures is preferably implemented to compare the measured and modeledintake-manifold pressures.

The pulsed triggering is preferably carried out using preselectablevalues of the frequency and the pulse duty factor with short openingdurations.

The working point is selected such that it is stable within predefinablelimits. The working point may lie either within idling operation or alsooutside of it.

In an advantageous embodiment of the method, the method steps areimplemented during triggering of the tank-ventilation value in activetank ventilation. Tank ventilation is used to desorb hydrocarbonspreviously adsorbed in the activated charcoal filter and must be carriedout at regular intervals due to the limited storage capacity of theactivated charcoal filter. Tank-ventilation is active for thepredominant part of engine operation. Utilizing phases of active tankventilation is advantageous insofar as no additional time must beexpended during engine operation for the diagnosis of thetank-ventilation valve, so that more time is available for otherdiagnostic functions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic representation of a tank-ventilation systemhaving a device for checking the operativeness of the tank-ventilationvalve.

FIG. 2 shows a schematic flow chart in block form for the device shownin FIG. 1 for checking the operativeness of the tank-ventilation valve.

DETAILED DESCRIPTION

A tank-ventilation system, shown in FIG. 1, includes a tank 10, anadsorption filter 20, such as an activated charcoal filter, which isconnected to tank 10 via a tank-connection line 12 and has a vent line22 able to be connected to the environment, as well as atank-ventilation valve (TVV) 30, which is connected on one side toadsorption filter 20 via a valve line 24 and on the other side to anintake manifold 40 of an internal combustion engine 50 via a valve line42.

Due to evaporation, hydrocarbons form in tank 10, which deposit inadsorption filter 20. To regenerate adsorption filter 20,tank-ventilation valve 30 is opened, so that air from the atmosphere isdrawn in through adsorption filter 20, because of the vacuum pressureprevailing in intake manifold 40, drawing the hydrocarbons deposited inadsorption filter 20 into intake manifold 40 and conveying them tointernal combustion engine 50.

A device 100, which is described in greater detail in connection withFIG. 2 in the following, is provided to check the operativeness oftank-ventilation valve 30.

Device 100 includes a first means 110 to determine the activationconditions as a function of rotational speed n_(mot) of the internalcombustion engine, which is detected by a sensor 52, of load signal r1as well as additional variables, such as engine temperature t_(mot).

As soon as the activation conditions have been met, a trigger means 120triggers tank-ventilation valve 30 in a pulsed manner using a frequencyto be preselected and a pulse duty factor to be predefined. In theprocess, the intake-manifold pressure is both measured and modeled.Then, a frequency analysis both of the measured intake-manifold pressureas well as the modeled intake-manifold pressure is implemented in ananalysis means 130, the frequency analysis being implemented as afunction of the pulse frequency using which tank-ventilation valve 30was triggered.

In another analysis means 140, a mixture analysis as a function of thelambda value is carried out. In an evaluation circuit part 150, thefrequency analysis of the measured intake-manifold pressure is thencompared to the frequency analysis of the modeled intake-manifoldpressure, taking the implemented mixture analysis into account. If thereis sufficient correlation of the two variables within preselectablelimits, it is assumed that tank-ventilation valve 30 operates properly.In this case, an evaluation signal ES One is output, for example. Ifcorrelation is lacking, an evaluation signal zero is emitted, which maylead to the conclusion that tank-ventilation valve 30 is not workingcorrectly.

The described method may also be implemented outside of idle operation.It must merely be carried out in a sufficiently stable working point.Since the method, unlike the known methods for checking theoperativeness of the tank-ventilation valve, does not require successivetriggering of the tank-ventilation over a relatively long interval up toits full opening, but uses a pulsed triggering at short opening timesinstead, the interference potential, such as a change in the rotationalspeed, able to be registered by the driver is only negligible.

The pulsed triggering is preferably carried out using preselectablevalues of the frequency and the pulse duty factor with short openingdurations. In this way, a partial opening of the tank-ventilation valvemay be simulated. For instance, the method may also be implemented veryadvantageously during triggering of tank-ventilation valve 30, whichoccurs anyway when tank ventilation is active.

1. A method for checking an operativeness of a tank-ventilation valve ofa tank-ventilation system of a motor vehicle, comprising: triggering thetank-ventilation valve in a pulsed manner in a predefinable workingpoint; measuring and modeling an intake-manifold pressure to produce ameasured intake-manifold pressure and a modeled intake-manifoldpressure; comparing the measured intake-manifold pressure to the modeledintake-manifold pressure to determine a correlation therebetween;assuming that the tank-ventilation valve is operative if the correlationis withing predefined limits; and assuming that the tank-ventilationvalve is defective if the correlation is outside the predefined limits,wherein: the method is performed during a triggering of thetank-ventilation valve for active tank ventilation.
 2. The method asrecited in claim 1, further comprising: performing a a frequencyanalysis of the measured intake-manifold pressure and the modeledintake-manifold pressure.
 3. The method as recited in claim 1, wherein:the pulsed triggering of the tank-ventilation valve is implemented usingpreselectable values of a frequency and a pulse duty factor with shortopening durations.
 4. The method as recited in claim 1, furthercomprising: selecting the preselectable working point such that thepreselectable working point is stable within the preselectable limits.5. The method as recited in claim 4, further comprising: selecting thepreselectable working point such that the preselectable working pointlies one of within and outside of idle operation.